Anyway to see list of preprocessor defined macros?

Question

I'd like to see all macros that are defined by the invocation of the compiler I'm using. Is there any way to do this? I have seen in the manual it says you can use cpp -dM but this doesn't work for me. Perhaps I'm doing something wrong?

When I run:

cpp -dM

I get no output at all from the preprocessor. If I try adding -dM as an option on gcc, I don't notice any difference.

Interlace

"Doesn't work for me" - please be more descriptive! – Larson

On my Linux computer, the output of cpp -dM < /dev/null | wc -l is 124, so there are 124 predefined values. cpp -dM < /dev/null | less shows me what they are. What is the output of those commands on your computer? – Blockbuster

Sorry I tried to clear it up a little – Interlace

Rob thank you I'll have to try and figure out how to do that from windows, which unfortunately I am stuck using. I'm using code sourcery cross compiler for arm. (A gcc port essentially) – Interlace

Answer 1

You can use:

gcc -dM -E - < /dev/null

Note that you can also get the compiler macros in addition with this command:

touch bla.c && gcc -dM -E bla.c

For example on my computer:

$ touch bla.c && gcc -dM -E bla.c | wc -l
486
$ gcc -dM -E - < /dev/null | wc -l
124
$

Unclothe

also useful are -xc, -xc++ and -std=... so you can compare language and dialect-specific definitions – Hunter

@Hunter actually I tried first gcc -xc -dM -E - < /dev/null for my second example, but this does not seem to work with -dM (same result as in the first example) – Unclothe

@Hunter ok so it has been fixed because it doesn't on my gcc-4.4.3/Linux – Unclothe

Answer 2

By default, cpp -dM will read its input file from standard input and write to standard output. Since you're not trying to preprocess any input, you can pass it the empty input using /dev/null:

# Option 1
cpp -dM < /dev/null
# Optio n2
cpp -dM /dev/null

On Windows, you can use the NUL pseudofile instead of /dev/null.

Atombomb